The present invention relates to electrical wiring boxes. More particularly, it is concerned with electrical wiring boxes having factory-installed mounting elements associated therewith for permitting the quick and easy mounting of an electrical device within a wiring box in a field installation.
At the present time electrical devices such as receptacles and switches are most commonly mounted within electrical wiring boxes by means of screws associated with the electrical devices and threaded into openings provided in tabs or bosses of the wiring boxes. Since the screws are usually of fine pitch and of considerable length, to accommodate several possible thicknesses of wallboard or paneling, considerable time is required to completely thread a pair of the screws into the tabs or bosses of a wiring box to tightly secure an electrical device to the wiring box. As a result, and in the interest of reducing escalating labor costs, it has been found highly desirable to reduce the time and effort required to mount electrical devices within wiring boxes. Numerous attempts have been made and several proposals offered directed to a solution of the above-stated problem. A review of many of these proposals is provided in U.S. patent application Ser. No. 712,145 filed Aug. 6, 1976 by William O. Arnold and David W. Kinney entitled "Electrical Wiring Box" and assigned to the assignee of the present application.
An electrical wiring box having a pair of factory-installed mounting elements associated therewith for permitting the quick and easy mounting of an electrical device within the wiring box is described and claimed in the aforementioned patent application. The wiring box includes bosses each having a generally-rectangular opening countersunk therein for receiving a corresponding mounting element. Each of the mounting elements includes a central portion having a screw-receiving opening and a pair of abutment edge portions adjacent to the opening, a pair of spaced-apart side portions integral with the central portion, and a pair of deflective V-shaped flanges including thread-engaging portions integral with the side portions. When inserted into the associated openings, the edge portions of the central portions of the mounting elements abut against shoulders adjacent to the openings, thereby limiting the forward entry of the mounting elements into the openings, and the V-shaped flanges are positioned externally at the back ends of the openings in a manner so as to prevent removal of the mounting elements from the opening.
An electrical device is mounted within the wiring box in a field installation by simply inserting associated screws into the screw-receiving openings of the central portions of the mounting elements and pushing the screws into the region between the V-shaped flanges. As a result, the thread engaging portions of the flanges are caused to be deflected outwardly and, after the screws have been driven completely home, the thread-engaging portions come to rest between the threads of the screws, thereby firmly gripping onto the screws. The outward deflection of the V-shaped flanges by the screws further causes the mounting elements to be more completely fixed within their associated openings.
As shown and described in the aforementioned application, the thread-engaging surfaces at the opposed free ends of the thread-engaging portions are of generally semi-circular configuration. Alternatively, they may be flat or V-shaped. It has been found that with mass production of mounting elements having thread-engaging surfaces as described there may be a wide variation in the amount of torque which a mounting element can withstand upon further tightening of the screw by threading subsequent to pushing the screw into position.